The present invention refers to a device for counting bars that are being translated and, more precisely, refers to a worm-screw device, or the like, which makes it possible to separate reliably even narrow bars while they are moving, transversely to their own longitudinal axis of symmetry, along a special path, so as to enable precise counting of the said bars.
In the handling of bars, for example metal bars, in particular to form bundles containing a given number of bars, generally automatic devices are used to count the bars while they move along a specific path.
Such devices comprise, for example, a screw conveyor, which displaces the bars transversely with respect to their longitudinal axis of symmetry and is combined with counting means, for instance photoelectric means. Said device further comprises means, coupled to means for rotating the worm screw, for detecting the number of rounds, and a processing unit which stores the information on the diameters of the bars and on the pitch of the screw of the screw conveyor used. At the entrance to the screw conveyor, the bars, which up to then have been moved together in a group, are separated from one another and accommodated in the grooves of the worm screw, theoretically one for each groove. The screw is positioned at a slightly inclined angle with respect to the plane of the conveyor set upstream and is structured in such a way that the pitch is constant and approximately equal to the diameter of the bar in the starting area of the screw itself. In the central region of the screw, the pitch starts increasing, thus enabling separation of the bars for the subsequent counting phase. In the final part of the screw, i.e., in the region where counting takes place, the pitch of the screw becomes constant again.
In the following, the pitch of a traditional screw measured in a generic point along its length will be defined as xe2x80x9cnormal pitchxe2x80x9d.
The bars thus advance perpendicularly to their longitudinal axis, with a distance between them that is at least equal to the pitch of the worm screw. A counting system, for example consisting of a photoelectric device with interruption of ray, is used to determine the number of bars in transit. In the ideal hypothesis that each groove accommodates a single bar, the number of interruptions of the ray corresponds to the number of bars that have passed through.
However, it is possible, in particular for bars of small diameter, for two bars to end up in a single groove. In this case, if the lying plane of the bars is not parallel to the axis of the counting system, the time of interruption of the ray will be greater than what it would be if a single bar passed, so enabling a processing unit to establish that in fact two bars to be counted, instead of just one. If, instead, the lying plane of the bars is more or less parallel to the axis of the counting system, the measured interruption time of the ray will be largely similar to the one of a single bar, and consequently the total count would be wrong. Since very often two bars are translated in the same groove, it is possible to have a grossly wrong final count, and consequently the bundles formed would contain a number of bars substantially higher than the one intended, with evident problems of a management and economic nature.
The present invention aims at overcoming such drawbacks by proposing a device which enables a precise counting of the bars, whatever the number of bars accommodated in a single groove may be.
According to the present invention, a worm-screw device is provided, in which the screw has a helical thread, with one or more starting points, which defines, in any given plane passing through the longitudinal axis of the screw itself, a plurality of grooves or grooves in which are accommodated the bars to be displaced, in a direction roughly perpendicular to the said longitudinal axis, towards counting means having a specific axis of action for the identification and counting of said bars; in the worm-screw device the screw presents grooves with at least part of one wall having a variable pitch which increases more rapidly than the normal pitch.
The presence of a part of the wall of the groove characterized by a pitch which increases more rapidly than the normal pitch makes it possible, in the case where more than one bar is present in the same groove, to render the lying plane of the bars not parallel to the specific axis of the counting means.
According to a first embodiment of the invention, this characteristic is obtained by generating grooves presenting, for at least part of the screw length, a wall which, towards the bottom, is characterized by a step having a width that increases in the direction of advance of the bars.
The width (measured in the direction of bar advance) of the step, measured in the vicinity of the counting means, preferably has a value of at least 0.3 times the diameter of the bar.
According to a second embodiment of the invention, this characteristic is obtained by generating grooves that present, for at least part of the screw length, a wall having a roughly rectilinear profile which forms an angle, with respect to the bottom of the groove, that increases in the direction of advance of the bars.
The angle of the wall with respect to the bottom of the groove, in the vicinity of the counting means, preferably has a value of at least 110xc2x0.
Again, in any case the height of the said grooves is preferably at least 0.3 times the diameter of the bars that are to be counted.